SE-0513: API to get the path to the current executable

[xwu (Xiaodi Wu)]

@grynspan

The current implementation does not attempt to repair the string if it isn't valid Unicode.

What sorts of invalid are we talking about here?

@Michael_Ilseman

Swift's String type's native storage is guaranteed-valid-UTF8 for this reason.

However, if the input isn't actually valid, assuming validity leads to a new class of security concerns.

(Emphasis added.)

If valid UTF-8 cannot be guaranteed but the implementation must bypass validation for whatever reason (e.g., performance), then it seems this needs to be an unsafe API or it needs to use some foreign storage representation so that validation is lazily triggered where it matters.

[Edit: the implementation does seem to use validating APIs on String—which, unless I'm misunderstanding, means that this API does return nil if there's invalid UTF-8.]